The United States is condemning suicide bus bombings in southern Israel, saying a Palestinian crackdown against terrorist factions is long overdue. The twin attacks, for which the Islamic group Hamas claimed responsibility, killed at least 15 people and wounded about 100 others.

Secretary of State Colin Powell telephoned his Israeli counterpart, Foreign Minister Silvan Shalom, to express U.S. condolences to families of the bombing victims and to condemn the attacks "in the strongest terms."

State Department Spokesman Richard Boucher said there can be no excuse for the terror and violence the Israeli people have been forced to endure, and that Palestinian leaders need to take "immediate and credible" steps to end such activity.

"The time for excuses is long past," said Mr. Boucher. "We need to see actions that send a clear message that terrorism will not be tolerated. Attacks such as these not only kill innocent civilians, but they undermine the aspirations and the hopes of the Palestinian people as well."

Mr. Boucher confirmed that the State Department's chief Middle East diplomat, Assistant Secretary William Burns, will visit the region in early September for talks on the Israeli-Palestinian conflict and other issues including Iraq.